JP2009028938A - Surface protective film - Google Patents

Abstract

[PROBLEMS] To provide an adherend having an appropriate adhesive property even on an adherend having a rough surface, excellent slipperiness on the back, blocking resistance and unwinding properties (reducing unwinding tension and adherend). The surface protective film is also excellent in that it can be easily and quickly bonded without causing wrinkles or scratches.
The surface protective film of the present invention comprises at least a composite form of an adhesive layer and a back layer, and the adhesive layer comprises 65 to 90% by weight of an olefin crystal / ethylene butylene / olefin crystal block copolymer, a propylene copolymer. It consists of 30 to 4% by weight and 15 to 1% by weight of low density polyethylene, and the back layer consists of 60 to 90% by weight of propylene copolymer and 40 to 10% by weight of low density polyethylene.
[Selection figure] None

Description

  The present invention relates to a surface protective film used for preventing the adhesion and scratching of an adherend surface. More specifically, it has appropriate adhesive properties even on adherends with rough surfaces, including diffusion plates and diffusion films used in the field of optics, etc. The present invention relates to a surface protective film excellent in handling properties such as excellent blocking resistance and unwinding properties.

Surface protective films have been used to prevent the surface from getting dirty or scratched when processing or transporting synthetic resin plates, metal plates, coated coated steel plates, and various nameplates. ing.
In particular, in recent years, thin displays such as liquid crystal displays have come to be used frequently as display devices for personal computers and televisions. This thin display is composed of a number of optical films and optical resin plates made of synthetic resin. It is composed of Since such optical films and optical resin plates need to reduce defects such as optical distortion as much as possible, in order to prevent contamination and scratches on these surfaces during processing and transportation, a surface protective film Is becoming increasingly used.

  As such a surface protective film, one in which an adhesive layer is laminated and integrated on one surface of a base material layer made of a thermoplastic resin is used, and in use, is adhered to the surface of an adherend by the adhesive layer and is unnecessary. Since it is peeled and removed when it becomes, it has suitable adhesive properties for sticking to the adherend surface, and it peels easily when peeling, and does not contaminate the adherend surface, etc. Is required.

  In addition, these surface protective films are usually rolled up into a roll, but these rolls are pressure-bonded with a relatively strong adhesive force between the base material layer and the adhesive layer. The films were easily blocked, and had problems such as being difficult to peel off when the surface protective film was unwound during use. In particular, in the case where the adherend surface is rough and high adhesive strength is required, it has become a more prominent problem.

  In order to eliminate such a problem, a layer opposite to the adhesive layer (hereinafter referred to as “back layer”) is used for the purpose of reducing the force necessary for unwinding the surface protective film (hereinafter referred to as “unwinding tension”). In general, mold release treatment is applied. Conventionally, as the mold release treatment, a method of applying a release agent to the back layer in advance has been used. However, it is difficult to adhere the release agent firmly to the back layer so that it can be easily separated from the adhesive layer. For this reason, a method of undercoating a special release agent or corona-treating the back layer before applying the release agent has been used. However, such a mold release treatment has a problem that the coating process becomes complicated, the yield is further reduced, and the cost is increased.

  On the other hand, in the method for forming the adhesive layer, a method in which an adhesive material dissolved in a solvent is applied to the base material and formed is used. In order to achieve solvent-free adhesive layer while maintaining adhesion, a method of forming a base material layer and an adhesive layer by co-extrusion and simultaneously laminating has been proposed (Patent Document 1).

  However, in the co-extrusion method, some mold release treatment is necessary on the back surface of the base material layer, but the mold release treatment cannot be performed in advance, and the timing of the process is limited. Then, the method of carrying out the friction process of the base material layer back surface of the laminated body obtained by the coextrusion method with a roll, cloth, etc. is proposed (patent document 2). However, the effect of the friction treatment may vary depending on the composition of the base material layer, and the unwinding tension may not be reduced satisfactorily.

  In order to solve this problem, a method has been proposed in which a resin layer (back layer) obtained by adding and blending silicone fine particles to an olefin resin and an adhesive layer are directly or indirectly laminated and integrated (Patent Document 3). However, in such a method, there is a problem that silicone fine particles are partially captured by the adhesive layer due to the adhesive property of the adhesive layer, causing a contamination factor.

By the way, many proposals including the said patent document are made | formed about the method of forming a base material layer and an adhesion layer by a coextrusion method, and laminating | stacking simultaneously. For example, in Japanese Patent Application Laid-Open No. 2000-33671 (Patent Document 4), as a surface protection film for a coated vehicle body, it has an appropriate tackiness, and is easily peeled when peeled and does not contaminate the adherend surface. As a layer structure, a base layer composed of a mixed resin of polypropylene and polyethylene is proposed by laminating an adhesive layer mainly composed of olefin crystal, ethylene butylene, and olefin crystal block copolymer by a coextrusion method. The problem of difficulty in unwinding due to blocking at the time of unrolling is unavoidable, and a method of subjecting the back surface of the base material to friction treatment by an individual is adopted.
JP-A-61-103975 JP-A-2-252777 JP 2000-345125 A JP 2000-33671 A

  The present invention solves the above-mentioned problems, has an appropriate adhesive property even on an adherend having a rough surface, has excellent slipperiness on the back surface, blocking resistance, unwinding property (winding business trip) It is intended to provide an excellent surface protection film that reduces the force and can be easily and quickly bonded without causing wrinkles or scratches when bonded to the adherend. .

The present invention employs the following means in order to solve such problems. That is, the surface protective film of the present invention is a surface protective film comprising at least an adhesive layer and a back layer, and the adhesive layer is composed of 65 to 90% by weight of an olefin crystal / ethylene butylene / olefin crystal block copolymer, propylene-based. Copolymer 30-4% by weight and low density polyethylene 15-1% by weight, the back layer is made of propylene copolymer 60-90% by weight, low density polyethylene 40-10% by weight. Features.

  Preferably, in the surface protective film of the present invention, the adhesive layer has a surface roughness of 0.3 μm or more as an arithmetic average roughness (Ra) defined in JIS B0601-1994, and the back surface layer. The surface roughness is 0.8 μm or more in terms of the arithmetic average roughness (Ra).

More preferably, the propylene copolymer has a melt flow rate at 230 ° C. under a load of 2.16 kg / cm ² (hereinafter referred to as MFR under 230 ° C.) in the range of 5 to 40 g / 10 minutes, and The low-density polyethylene has a melt flow rate (hereinafter referred to as MFR at 190 ° C.) of 0.5 to 5 g / 10 min at 190 ° C. and a load of 2.16 kg / cm ² .

  The surface protective film of the present invention is characterized by having an intermediate layer mainly composed of a polyolefin resin between the adhesive layer and the back layer.

  Preferably, the intermediate layer comprises a mixed resin composition of a polyolefin-based resin different from the resin constituting the adhesive layer and the back layer, and the adhesive layer constituent resin and the back layer constituent resin. It is.

  According to the present invention, the above-mentioned problems are solved, the adhesive surface has an appropriate adhesive property even on an adherend having a rough surface, is excellent in slipperiness on the back surface, has blocking resistance, unwinding property (winding property) Providing a surface protection film with excellent reproducibility that reduces the tension and can be easily and quickly bonded without being wrinkled or scratched when bonded to an adherend. Can do.

The present invention will be described in detail below.
The present invention has the above-mentioned problems, that is, it has an appropriate adhesive property even for an adherend having a rough surface, is excellent in slipperiness on the back surface, has blocking resistance and unwinding properties (unwinding tension is reduced). The surface protection film that has been reduced and has excellent wrinkles and scratches when bonded to the adherend and can be bonded easily and at high speed) The present invention has been devised to solve this problem at once by adopting a composite form of an adhesive layer made of the above and a back layer made of a specific resin composition, and also roughening the adhesive layer.

  First, the requirements for the adhesive layer of the present invention are as follows. The pressure-sensitive adhesive layer of the present invention needs to contain 65 to 90% by weight of an olefin crystal / ethylene butylene / olefin crystal block copolymer (hereinafter abbreviated as CEBC). Is a polybutadiene block controlled to 25% by weight or less, and the ethylene butylene block is preferably a polybutadiene block in which the 1,2-vinyl structure is controlled to 25 to 95% by weight. As a specific block copolymer, trade name “DYNARON (registered trademark) 6200P” manufactured by JSR Corporation may be mentioned.

  The adhesive layer must contain 30 to 4% by weight of a propylene copolymer and 15 to 1% by weight of low density polyethylene.

  By making such an adhesive layer into the resin composition, the adhesive layer is roughened (the surface roughness of the adhesive layer described later is 0.3 μm or more as the arithmetic average roughness (Ra) defined in JIS B0601-1994). In addition, by developing a synergistic effect with the roughening of the back layer (the surface roughness of the back layer is 0.8 μm or more in terms of arithmetic average roughness (Ra)), an adherend having a rough surface can be obtained. For the first time, a surface protective film with moderate adhesive properties and excellent back-side slipperiness, blocking resistance, unwinding properties, etc. Is possible.

  The CEBC content is specified in the range of 65 to 90% by weight, and within such a range, it is appropriately selected so as to obtain appropriate adhesion in accordance with the surface state (roughness) of the adherend. However, the range of 70 to 90% by weight is preferable. When the content of CEBC is less than 65% by weight, the adhesion to the adherend having a rough surface is insufficient. On the other hand, when it exceeds 90% by weight, it is difficult to unwind due to blocking during unwinding. Occurs.

  The propylene-based copolymer is a copolymer of ethylene and / or α-olefin and propylene, but the comonomer content of ethylene and α-olefin is not particularly limited as long as it is in the range of 1 to 9 mol%. When the film is formed by the melt coextrusion method described later, the higher the comonomer content, the lower the melting point of the copolymer, and the ease of coextrusion and low temperature extrusion are possible. The comonomer content is more preferably in the range of 3 to 7 mol%.

  Examples of the α-olefin as the comonomer include butene-1, hexene-1, 4-methylpentene-1, and opten-1, and the copolymer includes ethylene-propylene copolymer, Preferred examples include butene-propylene copolymer and ethylene-butene-propylene terpolymer. Of these, ethylene-propylene copolymer is preferred.

  Further, the MFR at 230 ° C. of the propylene copolymer is preferably in the range of 5 to 40 g / 10 minutes. In particular, the MFR is more preferable because 20 to 40 g / 10 min can be extruded at a low temperature.

  In addition, the ratio in the adhesion layer of the said propylene-type copolymer is prescribed | regulated in the range of 30 to 4 weight%. When the proportion of the propylene-based copolymer increases, when the adherend is a rough surface, the adhesiveness decreases, and an appropriate adhesive force cannot be obtained. On the other hand, when the amount is small, the films easily block each other, and the unwinding property is inferior. The proportion of the propylene-ethylene and / or α-olefin copolymer in the adhesive layer is more preferably in the range of 24 to 8% by weight.

  Further, the adhesive layer of the surface protective film of the present invention is based on the fact that 15 to 1% by weight of low density polyethylene is contained in addition to the CEBC and the propylene-based copolymer. If the ratio of density polyethylene is small, the pressure-sensitive adhesive layer surface becomes smooth. On the other hand, if it is large, not only the desired pressure-sensitive adhesive properties are difficult to obtain, but also the pressure-sensitive adhesive layer becomes too rough or locally uneven. There is. Preferably, it is the range of 6 to 2 weight%.

  The content ratio of the propylene copolymer and low density polyethylene contained in the adhesive layer is preferably in the range of 7: 3 to 9: 1.

  The MFR at 190 ° C. of such low density polyethylene is preferably in the range of 0.5 to 5 g / 10 minutes, and the difference between the MFR at 190 ° C. of the low density polyethylene and the MFR at 230 ° C. of the propylene copolymer is large. More preferably (for example, the difference is 10 g / 10 min or more, preferably 20 g / 10 min or more), since the roughening effect is remarkably exhibited.

  The surface roughness of the pressure-sensitive adhesive layer of the present invention formed by such a resin structure is preferably 0.3 μm or more as the arithmetic average roughness Ra specified in JIS B0601-1994. As the surface roughness Ra of the adhesive layer is larger, the blocking property is improved in combination with the roughening of the back layer, and more preferably Ra is 0.35 μm or more. Furthermore, it is more preferable that the maximum roughness Ry is 1.8 μm or more.

  Next, the requirements for the back layer of the present invention are as follows. The back layer of the present invention is composed of 60 to 90% by weight of a propylene copolymer and 40 to 10% by weight of low density polyethylene, and the propylene copolymer has a high ethylene content as described above. The melting point of the copolymer can be lowered, the coextrusion is easy, and low temperature extrusion is possible, so the comonomer content is more preferably in the range of 3 to 7 mol%. In addition, when adding heat resistance to a back surface layer, it can also select suitably so that this comonomer content may be decreased and desired heat resistance may be acquired.

  Further, the MFR at 230 ° C. of the propylene copolymer is preferably in the range of 5 to 40 g / 10 minutes. In particular, those having a MFR of 20 to 40 g / 10 min are more preferred because they can be extruded at low temperature and the back layer is easily roughened by combining with low-density polyethylene described later.

The low-density polyethylene constituting the back layer is also preferably in the range of MFR 0.5 to 5 g / 10 min at 190 ° C. as described above. The low-density polyethylene of the present invention preferably has a density in the range of 0.910 to 0.929 g / cm ³ , and if the density is higher than this, the resin falls off in rubbing with a metal roll or rubber roll. It easily causes white powder generation, and if it is low, it becomes difficult to obtain the desired surface roughness.

  The propylene copolymer and the low density polyethylene may be the same as or different from those constituting the adhesive layer, but the type of resin used is reduced when the same resin is used. To preferred.

  As for the surface roughness of the back layer of the present invention formed by such a resin structure, the arithmetic average roughness Ra according to JIS B0601-1994 is preferably 0.8 μm or more. As the surface roughness Ra of the back layer is larger, the blocking property is improved in combination with the roughening of the adhesive layer, and more preferably Ra is 1.0 μm or more. The maximum roughness Ry is more preferably 5.0 μm or more.

  Next, the composite form of the present invention is as follows.

  The surface protective film of the present invention is composed of a composite form of at least the adhesive layer and the back layer, but may be a two-layer laminated film of the adhesive layer and the back layer. However, it is more preferable to have a three-layer laminated film structure having an intermediate layer mainly composed of a polyolefin-based resin between the adhesive layer and the back layer.

  Examples of the polyolefin resin mainly constituting the intermediate layer include, for example, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-α-olefin copolymer, polypropylene, ethylene-propylene copolymer. Polymer (random copolymer and / or block copolymer), α-olefin-propylene copolymer, ethylene-ethyl (meth) acrylate copolymer, ethylene-methyl (meth) acrylate copolymer, ethylene-n- A butyl (meth) acrylate copolymer, an ethylene-vinyl acetate copolymer, etc. can be mentioned. These may be used alone or in combination. The α-olefin is not particularly limited as long as it can be copolymerized with propylene. For example, butene-1, hexene-1, 4-methylpentene-1, octene-1, pentene-1, heptene-1 Etc. Especially, it is preferable that it is a polyolefin-type resin different from the resin which comprises the said adhesion layer and back layer.

  In the surface protective film of the present invention, the intermediate layer may be used by adding and mixing an adhesive layer constituting resin and / or a back layer constituting resin to the above-mentioned polyolefin resin. In general, when a film is formed by melt coextrusion, the non-uniform thickness at the end is slit and removed by a slitting process, etc., but by using this part for the intermediate layer, the amount of raw material used can be reduced. Is the preferred method.

  The intermediate layer contains fillers such as talc, stearamide, calcium stearate, lubricants, antioxidants, ultraviolet absorbers, pigments, antistatic agents, nucleating agents, etc., as long as their physical properties are not impaired. You may add suitably. Moreover, you may add these individually or in combination of 2 or more types.

  Moreover, embossing etc. can be given to a back surface, and it can print as needed as well as coloring by pigment addition.

Now, a method for producing the surface protective film of the present invention will be described.
The method for producing the surface protective film of the present invention is not particularly limited. For example, as a back layer constituting resin, a mixed resin composition comprising 60 to 90% by weight of a propylene copolymer and 40 to 10% by weight of low density polyethylene, As the adhesive layer constituting resin, a mixed resin composition comprising CEBC 65 to 90% by weight, propylene-based copolymer 30 to 4% by weight and low density polyethylene 15 to 1% by weight, and more preferably, as the intermediate layer constituting resin, A resin composition comprising a polyolefin resin is melt-extruded from individual extruders, laminated and integrated in a die, and so-called three layers are co-extruded to form a back layer, an intermediate layer, and an adhesive layer. After that, the method for producing the surface protective film by winding in a coil shape, the back layer, the intermediate layer, and the adhesive layer were individually melt extruded. In, and a method of integrally laminating the adhesive layer on the back layer and / or intermediate layer and the like by a lamination method. In the former, a known method such as an inflation method or a T-die method is used, and in the latter, dry lamination or a melt extrusion method or extrusion coating method using a T-die can be used, but the thickness accuracy is excellent. From the viewpoint of controlling the surface shape, the hot melt coextrusion method by the T-die method is preferable from the viewpoint of quality and economy.

The thickness of the surface protective film of the present invention varies depending on the thickness of the adherend and the required quality level of the adherend, but in general, it can be appropriately selected in the range of 20 to 100 μm from the viewpoint of moldability and ease of use.
The thickness of each of the adhesive layer, the intermediate layer, and the back layer may be appropriately adjusted according to the required level as described above. For example, in the laminated film composed of two layers, the back layer Is adjusted to 15 to 80 μm, and the pressure-sensitive adhesive layer is adjusted to about 5 to 40 μm. Moreover, in the 3 layer laminated film which is a preferable form, a back surface layer is adjusted to 2-10 micrometers, an intermediate | middle layer 13-70 micrometers, and an adhesive layer is adjusted to 5-40 micrometers.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to these Examples. In the examples and comparative examples, “parts” and “%” are based on weight unless otherwise specified. Moreover, the measuring method and evaluation method of various physical property values are shown below.

-Surface roughness The surface roughness is a surface roughness profile measuring machine (Surfcom 1400A) manufactured by Tokyo Seimitsu Co., Ltd., in accordance with JIS B0601-1994, with a cutoff value (λc) of 0.8 mm and a reference length. (L) 0.8 mm, measured length of 4 mm in the lateral direction of the film, averaged by measuring 10 times at intervals of about 1 mm in the longitudinal direction (machine direction), arithmetic average roughness (Ra) and maximum roughness (Ry) ) (Unit: μm).

(2) Sample pressing sample (A Yasuda Seiki Seisakusyo Co., Ltd.) was used with the sample samples of Examples and Comparative Examples stored and adjusted for 24 hours under conditions of 23 ° C. and 50% humidity. Using a special press roller, a pasting pressure of 9,100 N / m and a pasting speed of 300 cm / min were used. Thereafter, the sample was stored for 24 hours under conditions of a temperature of 23 ° C. and a humidity of 50%, and then used for each measurement and evaluation.

(3) Using a tensile strength tester (Orientec “Tensilon” universal tester), the adhesive strength was measured at a tensile speed of 300 mm / min and a peeling angle of 180 °.

(4) Adhesiveness The adhesion state of the adherend and the sample sample was observed with the naked eye, and the following determination was made.

○: Completely adhered Δ: Only 1 part is poorly adhered and 1 part of the sample film is floating (within an area ratio of 30% or less) ×: The film is floated from the adherend at an area ratio of 70% or more (5) After peeling off the sample film from the contaminated adherend, spot light was applied to the surface of the adherend in the dark room, and the contamination state of the surface was visually observed to make the following determination.

○: No contamination △: Mild contamination ×: Contaminated

Examples 1-3
The constituent resin of each layer was prepared as follows.

As the adhesive layer resin, CEBC (trade name “DYNARON ^™ 6200P” manufactured by JSR Corporation, referred to as Resin 1) 65% by weight, ethylene-propylene with an ethylene content of 5% by weight at 230 ° C. and an MFR of 30 g / 10 min. A resin composition comprising 28% by weight of a copolymer (denoted as resin 2) and 7% by weight of low-density polyethylene (denoted as resin 3) having a density of 190 ° C. MFR 2 g / 10 min and a density of 0.92 g / cm ^{3 in} a Henschel mixer. Mix uniformly (Example 1).

  In the same manner as in Example 1, a resin composition consisting of 80% by weight of CEBC, 16% by weight of ethylene-propylene copolymer and 4% by weight of low density polyethylene was uniformly mixed in a Henschel mixer (Example 2).

  In the same manner as in Example 1, a resin composition consisting of 90% by weight of CEBC, 8% by weight of ethylene-propylene copolymer and 2% by weight of low density polyethylene was uniformly mixed in a Henschel mixer (Example 3).

As the back layer resin, ethylene-propylene copolymer 88% by weight of ethylene content 5% by weight at 230 ° C. MFR ³⁰ g / 10 min and 190 ° C. MFR 2 g / 10 min, density 0.92 g / cm ³ of low density polyethylene 12% by weight % Of the resin composition was uniformly mixed with a Henschel mixer (Example 1).

  In the same manner as in Example 1, a resin composition composed of 80% by weight of ethylene-propylene copolymer and 20% by weight of low density polyethylene was uniformly mixed in a Henschel mixer (Examples 2 and 3).

  Next, using the prepared resin for each layer (Examples 1, 2, and 3), a T-die type composite having a die width of 2400 mm having two extruders of φ90 mm (for adhesive layer) and φ115 mm (for back layer) Using the film forming machine, the prepared resin composition is introduced into each extruder, and the discharge amount of each extruder is adjusted so that the adhesive layer thickness ratio is 30% and the back layer thickness ratio is 70%. The film was extruded at an extrusion temperature of 200 ° C. to form a two-layer laminated film having a film thickness of 50 μm, and was wound up into a roll once.

  Next, the film wound up in a roll shape was subjected to a slitting machine and finished to a size of 1000 mm in width and 600 m in length, and film samples wound up in the roll shape of Example 1, Example 2 and Example 3 were obtained.

  The films of Examples 1 to 3 thus obtained do not need to be subjected to a treatment such as a mold release treatment when a product having a predetermined width is obtained with a slitting machine, and are easily sent out to the slitting machine without any resistance (winding). And no blocking was observed. When blocking occurs, when the adhesive layer and the back surface layer are peeled off, there is a beveling and peeling sound, but it was confirmed that there was no such peeling noise and the film was unrolled very smoothly.

In order to evaluate the characteristics of the obtained films of Examples 1 to 3, even when the film was rewound for sample cutting, no blocking was observed as in the above, and the film could be smoothly rewound to obtain a cut sample. did it.
Thereafter, Table 1 shows the results of evaluation of various characteristics using the sample sample.

  Here, the adhesion characteristic-1 is an evaluation of the adhesion characteristic using a polycarbonate plate having a surface roughness (Ra) of 0.6 μm and a thickness of 2.0 mm as an adherend.

Adhesive property-2 is an evaluation of the adhesive property by replacing the adherend with a smooth (Ra 0.02 μm) polycarbonate plate having a thickness of 2.0 mm.
Example 4
As the adhesive layer resin, the same resin composition as in Example 2 was used. As the back layer resin, the same resin composition as the back layer resin composition used in Example 2 and Example 3 was prepared. As the intermediate layer resin, 20% by weight of the adhesive layer resin of Example 2, 5% by weight of the back layer resin of Example 2, and homopolypropylene at 230 ° C. with an MFR of 7.5 g / 10 min (referred to as resin 4). ) A resin composition comprising 75% by weight was uniformly mixed with a Henschel mixer. Next, using a three-layer composite film forming machine having three extruders, the resin composition of each layer was introduced into each extruder (each extrusion temperature 190 ° C.), the adhesive layer thickness ratio was 25%, and the intermediate layer thickness ratio was After adjusting the discharge amount of each extruder to 67% and the back layer thickness ratio of 8%, extrusion was performed from a composite T die to form a three-layer laminated film having a film thickness of 40 μm, and then wound into a roll. Thereafter, the film once wound up in a roll shape was subjected to a slitting machine to finish a width of 1000 mm and a length of 1000 m, and a film product rolled up into a roll shape was obtained.

  As in Examples 1 to 3, when a product having a predetermined width was obtained with a slitting machine, it could be easily sent out (unwinded) to the slitting machine without any resistance, and no blocking was observed. Although the obtained roll-shaped film product was rewound and the blocking property was confirmed, blocking was not recognized at all. Further, when the surface roughness was measured for each of the adhesive layer and the back layer, the adhesive layer surface roughness Ra was 0.42 μm and Ry was 2.08 μm, and the back layer surface roughness Ra was 1.08 μm and Ry was 5.43 μm. As the adherend, a polycarbonate plate having a surface roughness (Ra) of 0.60 μm and a thickness of 2.0 mm was used, and when the tackiness was evaluated, the adherence to the adherend was good and the tackiness was 0.68N. / 50 mm. Further, after the film was peeled off, the surface of the adherend was observed, but no contamination was observed. Other characteristic evaluation results were as shown in Table 2 and there was no problem.

Comparative Example 1
As the adhesive layer resin, CEBC 60% by weight, ethylene content 5% by weight at 230 ° C. MFR 30 g / 10 min, ethylene-propylene copolymer 32% by weight, and 190 ° C. MFR 2 g / 10 min, density 0.92 g / cm ³ A laminated film having a thickness of 50 μm was formed under the same conditions as in Example 2 except that a resin composition consisting of 8% by weight of low density polyethylene was uniformly mixed in a Henschel mixer, and wound into a roll. I took it. Although blocking was not recognized by the obtained film, when it bonded together on the roughened polycarbonate board of surface roughness Ra0.60 micrometer, it floated and satisfactory adhesiveness was not obtained (adhesion determination: X).
Comparative Example 2
A laminated film having a thickness of 50 μm was formed under the same conditions as in Example 2 except that a resin composition consisting of 100% by weight of CEBC was used as the adhesive layer resin, and was wound into a roll.

After that, when I tried to unwind the film once wound up on a slitting machine, the adhesive layer and the back layer were firmly adhered and blocked, and when unreasonably unwound, A peeling sound was made, and not only the adhesive layer resin was partially captured by the back layer, but also the unwinding tension was too high and the film was stretched. In addition, in order to avoid blocking, after film formation, the film was carefully sampled without being wound into a roll, and when the surface roughness of the film was measured, the adhesive layer Ra was 0.46 μm and the back layer Ra was 1.04 μm. .

Comparative Example 3
As the adhesive layer resin, a resin composition comprising 80% by weight of CEBC and 20% by weight of an ethylene-propylene copolymer having an ethylene content of 5% by weight at 230 ° C. and an MFR of 30 g / 10 minutes is used in a Henschel mixer. A laminated film having a thickness of 50 μm was formed under the same conditions as in Example 2 except that the film was wound into a roll.

After that, when the film once wound was applied to a slitting machine, an attempt was made to unwind. As a result, the adhesive layer and the back layer were considerably adhered and blocked, and the film could not be unwound stably. In order to avoid blocking, after film formation, the film was carefully sampled without being wound into a roll, and when the surface roughness of the film was measured, the adhesive layer Ra was 0.27 μm and the back layer Ra was 1.05 μm. .
Comparative Example 4
As adhesive layer resin, CEBC 88% by weight, ethylene-propylene copolymer 2% by weight of ethylene content 5% by weight MFR 30 g / 10 min at 230 ° C., and 190 ° C. MFR 2 g / 10 min, density 0.92 g / cm ³ low A laminated film having a thickness of 50 μm was formed under the same conditions as in Example 2 except that a resin composition consisting of 10% by weight of density polyethylene was uniformly mixed in a Henschel mixer, and wound into a roll. It was.

  Thereafter, the film once wound up was put on a slitting machine so as to be unwound, and this film was in an unstable unwinding state because blocking was observed in the adhesive layer and the back layer.

In addition, in order to avoid blocking, after film formation, the film was carefully sampled without being wound into a roll, and when the surface roughness of the film was measured, the adhesive layer Ra was 0.29 μm and the back layer Ra was 1.06 μm. .
Comparative Example 5
A thickness of 50 μm under the same conditions as in Example 2 except that a resin composition comprising 100% by weight of an ethylene-propylene copolymer having an ethylene content of 5% by weight at 230 ° C. and an MFR of 30 g / 10 min at 230 ° C. is used. Was laminated and wound up into a roll.

  After that, when I tried to unwind the film once wound up on a slitting machine, the adhesive layer and the back layer were firmly adhered and blocked, and when unreasonably unwound, A peeling sound was made, and not only the adhesive layer resin was partially captured by the back layer, but also the unwinding tension was too high and the film was stretched.

  In addition, in order to avoid blocking, after film formation, the film was carefully sampled without being wound into a roll, and when the surface roughness of the film was measured, the adhesive layer Ra was 0.25 μm and the back layer Ra was 0.17 μm. .

  The surface protective film of the present invention is frequently used not only for the prevention of dirt adhesion and scratching during processing and transportation of synthetic resin plates, metal plates, coated coated steel plates, various nameplates, etc., but also for thin displays such as liquid crystal displays in recent years. It can be preferably used as a surface protective film for preventing various kinds of optical films made of synthetic resins and optical resin plates from being used and preventing surface contamination and scratches during transportation.

Claims (6)

A surface protective film comprising at least an adhesive layer and a back layer, the adhesive layer comprising 65 to 90% by weight of an olefin crystal / ethylene butylene / olefin crystal block copolymer, 30 to 4% by weight of a propylene copolymer, and A surface protective film comprising 15 to 1% by weight of low density polyethylene, and the back layer comprising 60 to 90% by weight of a propylene copolymer and 40 to 10% by weight of low density polyethylene. The surface protective film according to claim 1, wherein the adhesive layer has a surface roughness (Ra) of 0.3 μm or more, and the back layer has a surface roughness (Ra) of 0.8 μm or more. The surface protection film according to claim 1 or 2, wherein a melt flow rate of the propylene copolymer at 230 ° C and a load of 2.16 kg / cm ² is in a range of 5 to 40 g / 10 minutes. The low-density 190 ° C. Polyethylene, surface protective film according to claim 1 melt flow rate at ² under a load 2.16 kg / cm is 0.5 to 5 g / 10 min. The surface protective film according to any one of claims 1 to 4, further comprising an intermediate layer mainly composed of a polyolefin resin between the adhesive layer and the back surface layer. The said intermediate | middle layer is a composition which consists of mixed resin of polyolefin resin different from resin which comprises the said adhesion layer and back layer, and resin which comprises the said adhesion layer and / or back layer. Surface protective film.